The Rosharon town site went unnamed during its early years. The area was settled by cotton and sugar plantations before the Civil War. Once the Houston Tap and Brazoria Railway (Columbia Tap) was completed in 1859, the Rosharon stop on the train line was given the name Masterson's Station, after a nearby plantation owned by Thomas G. Masterson (ca. 1813–1884). Rosharon was known locally by trainmen as "Buttermilk Station" because an early resident was known to bring a bucket of buttermilk and a dipper to the railroad station to give the engineer and crew a drink.
George Wetmore Colles, Jr. (1871–1951), an electrical and mechanical engineer educated at Yale University (BA 1892) and the Stevens Institute of Technology, bought property in the area around 1900 and called his estate the Rose of Sharon Garden Ranch after the many Cherokee Roses (Rosa laevigata) that grew there. Colles also designed the community water system.